Powerhead interchangability on 1956 Johnson 30hp lower unit

[PatrickMFrank]

Hey Guys:

I have a 1956 Johnson 30hp, which has a 40hp powerhead on it. Would anyone know my options of what powerheads (size and year) will fit on this lower unit?

 

[F_R]

Re: Powerhead interchangability on 1956 Johnson 30hp lower unit

How do you know it's a 40hp? Well, anyhow, the 40hp Gale motors (all) will bolt up. So should the Evinrude and Johnsons, 1971-74. The 28 and 33hp motors from the 1960's will fit too. 40hp Evinrude and Johnsons 1960-70 will NOT fit.

Be aware that there were many changes down through the years so you might be in for some suprprises as you make the swap.

EDIT!!!!! I take it all back. Check the cylinder head on these guys to see if they have the brackets for your Johnson hood mounts.

 

[PatrickMFrank]

Re: Powerhead interchangability on 1956 Johnson 30hp lower unit

Thanks for your help. In regards to the 40hp, my grandfather, who built the motor, told me it was a 40hp powerhead. It is definitely not the 30 hp. Differences include a different throttle control arm, with more spark advance travel, compression release on the head, a carb with the high speed jet connected to an adjustment knob next to the low speed jet, as per later motors. I know what the bore and stroke for the cylinders are, but am reluctant to pull the heads unless I know I can find gaskets for it. The spark plug centers are 3 1/2 " apart, if this helps. In regards to the hood mounts, the front mounts are part of the generator and starter mounts, but the back have concave bosses in the cylinder head, in which mushroom-shaped rubber mounts on the hood rest against. I may just try to replace the coils, points, and wiring to see if it still runs (it did when put into storage in the early 80s) and go from there. If there are problems, I'll look for a 70's powerhead, and examine it for hood mounting problems. Thanks again!

 

[Chinewalker]

Re: Powerhead interchangability on 1956 Johnson 30hp lower unit

That sounds more like a 1957/1958 35hp powerhead, as the 40 never came with the cowling mounts in the cylinder head, and a 35 cylinder head won't fit a 40...

- Scott

 

[BoatBuoy]

Re: Powerhead interchangability on 1956 Johnson 30hp lower unit

Also, did the 40 ever have compression relief?

 

[F_R]

Re: Powerhead interchangability on 1956 Johnson 30hp lower unit

Yep, 35hp. Compression relief, adjustble high speed jet. OR it Could be a 1961 Gale 40 which had the above items and the concave hood mounts. Hard to say without measuring the bore.

 

[PatrickMFrank]

Re: Powerhead interchangability on 1956 Johnson 30hp lower unit

Thanks for all your help, guys. I had wondered about the 35hp, as he had two 35's on a boat shortly before his death. I'll go ahead and pull the powerhead and confirm the bore size, and go from there. I just located parts for older outboards at vintageoutboards.com, with a number of other links, so seals and gaskets should'nt be a problem. Now I know where to go for expert advice! Thanks again!

 

[BoatBuoy]

Re: Powerhead interchangability on 1956 Johnson 30hp lower unit

Yep, 35hp.

I know the '57, '58, and '59 35hp J/E had compression relief, but didn't they discontinue that for the subsequent J/E 40's? ('56 30hp didn't have it either)

 

[Chinewalker]

Re: Powerhead interchangability on 1956 Johnson 30hp lower unit

1960 40hp Johnrudes had the compression relief. I think it was phased out in 1961...
- Scott

 

[F_R]

Re: Powerhead interchangability on 1956 Johnson 30hp lower unit

Just for the record, here is the 1961 Gale 40

 

[CATransplant]

Re: Powerhead interchangability on 1956 Johnson 30hp lower unit

Hang on to that compression relief. If you ever need to rope start it, you'll be glad they're there.

Actually, if that thing ran well when it was put away, I'd check the compression, put in a carb kit, replace the impeller, pull the flywheel and check the points and coils, and give it a try. It may even have the newer coils in it already, if it was worked on before being stored.

Don't make work for yourself. I bought a 1958 RDS-20...a 35hp very similar to yours. It hadn't run for years. I did pull the flywheel, and found new coils and points in there. Compression was OK. Just for grins, I left the carb on there and didn't kit it. Well, when I hooked up the fuel, pumped the bulb, pushed the electric choke button and cranked it, it fired right up. It idled fine and pushed my soggy trihull to about 25mph. Ran like a top as long as I had it.

And, it had the compression release stuff. Just for grins, I rope-started it a few times. A tough nut when it was cold, but it would fire up with about a half pull when it was warmed up.

 

[PatrickMFrank]

Re: Powerhead interchangability on 1956 Johnson 30hp lower unit

I may do just that. When I put the motor in storage, I ran a high oil content gas to lubricate the bearings, and drained the carb, then filled the chambers with WD-40. The motor turns over fine, shifts OK, but the wiring has had it. I'll get some new points, impeller, plugs, plug wires, and rewire everything else, cross my fingers and try to fire it up. This motor does'nt weigh much more than my 96 Johnson 15, and on my Alweld 14 V-bottom, it should really push it. Thanks for the advice!